1. Field of the Invention
The invention relates to a process for the hydrolysis and condensation of alkyl/aryl-trichlorosilanes which may contain up to 40 mole % of dialkyl or diaryl or alkylaryl-dichlorosilanes.
2. Description of the Prior Art
The hydrolysis of halogen silanes usually takes place in open systems of the kind wherein halogen silanes are added to water which is already present. However, this method does not allow alkyl/aryl-trichlorosilanes or silane mixtures, which contain the trichlorosilanes predominantly, to be hydrolized without gelling the reaction products. "Chemie and Technologie der Silicone" (Chemistry and Technology of the Silicones) by Walter Noll, published by Chemie GmbH in 1968, Page 164, states that methyltrichlorosilane forms highly cross-linked gel-like or powder-like polymers on being hydrolyzed with water. The other know processes of hydrolysis are also dealt with in this book. It is reported, for example, that trichlorosilanes can be hydrolyzed in the presence of larger amounts of solvents which dilute the reaction medium. However, when using trichlorosilanes having bulky organic groups and ether as the solvent, only low molecular weight cyclic siloxanes are primarily obtained.
The hydrolysis of trichlorosilanes can also be carried out with water/alcohol mixtures. In this instance also, the concomitant use of solvents is customary so that this process is expensive and does not completely avoid the danger of gelling when high proportions of trichlorosilanes are present in the silane mixture.
The well known "reverse hydrolysis" process in which water is added to halogen silanes also leads to complete gelling of the reaction products when trichlorosilanes are hydrolized, even in the presence of solvents.
Hydrolysis at lower temperatures, e.g., at -73.degree. C. in ether leads to low molecular weight chlorosiloxanes with a high residual chlorine content. The ratio of chlorine to silicon in these compounds is greater than 1.
It is a particular disadvantage of these processes that portions of the halosilane starting materials are carried along with the hydrogen chloride liberated in the reaction. As a consequence, the composition of the reaction mixture in relation to the chlorosilane starting material changes uncontrollably during the reaction so that the reproducibility of the products manufactured is impaired.
The gaseous HCl which escapes cannot be utilized further since it is contaminated by silanes. It must therefore be neutralized. The conventional processes are therefore disadvantageous since the waste air and water produced must be further treated before disposal. Also, the chlorine of the chlorosilane starting materials is lost for further use. Also, the halogen silanes which are carried off are deposited and collected on various surfaces of the equipment, especially in the waste air lines, where they are hydrolyzed by the moisture in the air. In addition to the waste of the materials, the collection of these materials creates the danger of further corrosion.